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1876. Li, D., and J. Zhao, “Surface biomedical effects of plasma on polyetherurethane,” J. Adhesion Science and Technology, 9, 1249-1261, (1995).

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N2 and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N2 and Ar plasma treatments, and N2 plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N2 and Ar plasma treatments broke some of the CSingle BondO and CDouble BondO bonds at the surface and resulted in oxidation of the surface.

1930. Li, L.-H., C. Macosko, G.L. Korba, A.V. Pocius, and M. Tirrell, “Interfacial energy and adhesion between acrylic pressure sensitive adhesives and release coatings,” J. Adhesion, 77, 95-123, (Oct 2001).

The interfacial adhesive behavior between acrylic pressure sensitive adhesive-like networks (PSA-LNs) and poly(vinyl N-alkyl carbamate) release coatings was studied using a contact mechanical method and peel tests. Surface energy and interfacial energy were directly measured in JKR tests using a novel sample construction. The surface energy of the poly(vinyl N-alkyl carbamates) was found to be around 20 mJ/m2. Interfacial energies between PSA-LNs and the release coatings were found to be quite high – between 7 and 24 mJ/m2. Changes in adhesion dynamics were governed by acid-base interactions between the carbamate in the release coating and the acid groups in the PSA-LN. The length of the alkyl chain in the release coating moderated this effect. We also found a correlation between fundamental adhesion energy and peel strength. Examination of this phenomenon provides a basis for understanding the poor storage stability of PSA tapes made using alkyl carbamates and acid-containing PSAs.

1932. Li, L.-H., M. Tirrell, G.A. Korba, and A.V. Pocius, “Surface energy and adhesion studies on acrylic pressure sensitive adhesives,” J. Adhesion, 76, 307-334, (Aug 2001).

The surface energy and adhesion dynamics of pressure sensitive adhesives-like networks (PSA-LNs) as mimics for PSAs were studied using JKR-based contact mechanics and peel tests. Acrylic acid (AA) was co-polymerized with 2-ethyl hexyl acrylate (2-EHA) and 1,6-hexane diol diacrylate (HDDA) to create PSA-LNs. The measured surface energy (27 to 31 mJ/m2) was sensible as surmised from their structure. Acrylic acid content increases the surface energy, threshold adhesion energy and adhesion hysteresis of PSA-LNs. Measurements of adhesion dynamics showed a dependence of adhesion energy to the 0.6–0.8 power of crack speed, depending upon the model chosen for analysis of the data. When compared with actual pressure-sensitive adhesive tape peel tests, the adhesion dynamics data predicted the peel strength. This study shows a direct relationship between threshold adhesion energy, crack propagation mechanics and peel strength measurements.

1738. Li, Q., P.P. Tsai, S. Nourgostar, Z. Chen, J.R. Roth, et al, “Processing of films and fabrics with the MOD III roll-to-roll one atmosphere uniform glow discharge plasma (OAUGDP) reactor,” in 16th IEEE International Pulsed Power Conference, IEEE, Jun 2007.

Atmospheric pressure plasma treatment has unique advantages over vacuum treatment for such industrial applications as surface energy ehancement of materials, cleaning, decontamination, and sterilization of surfaces, surface etching, plasma chemical vapor deposition (PCVD), and related tasks. The MOD VIII plasma reactor system has been developed to provide roll-to-roll surface treatment of fabrics and films using a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP®) operating in air. Webs can be continuously and uniformly treated by proper control of gas flow; electrode configuration; plasma voltage, current, and frequency; fabric speed; and fabric tension.

711. Li, S., D.Y. Wu, W.S. Gutowski, and H.J. Griesser, “Surface dynamics and adhesive bonding of plasma-treated polyolefins and fluoropolymers,” Presented at First International Congress on Adhesion Science and Technology, Oct 1995.

1801. Li, S.K., R.P. Smith, and A.W. Neumann, “Wilhelmy technique and solidification front technique to study the wettability of fibres,” J. Adhesion, 17, 105-122, (Aug 1984).

The strength of fibre-reinforced materials depends heavily on the adhesion between the fibre and the resin. To predict the bond strength of the adhesion, it is desirable for the surface tension of the fibre to be known. Two independent methods, the Wilhelmy balance method and the solidification front method, were investigated. The fibres used for this investigation included a carbon fibre, Thornel 300®, and an aromatic poiyamide fibre, Kevlar.

In the Wilhelmy experiments three liquids, ethylene glycol, glycerol and distilled water were employed to measure the surface tensions of the test fibres. They were found to be 42.4 mJ/m2 and 43.7 mJ/m2 for the carbon fibre and Kevlar, respectively. These values agreed very well with the results obtained from the solidification front method, from which the carbon fibre was found to have a surface tension value of 41.8 mJ/m2 while that for Kevlar was 46.4 mJ/m2. Furthermore, error analysis has shown that the error limits of the experiments are within 5% of the resulting values. The reproducibility and accuracy of these two techniques indicate that they are viable for determining the surface tension of small diameter fibres.

2714. Li, X., M. Toro, F. Lu, J. On, A. Bailey, and T. Debies, “Vacuum UV photo-oxidation of polystyrene,” J. Adhesion Science and Technology, 30, 2212-2223, (2016).

Polystyrene (PS) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation and X-ray photoelectron spectroscopy detected a controlled increase in the atomic percentage of oxygen up to a saturation level of ca. 20 at% O. Initially, C–O and carbonyl groups are observed due to the formation of alcohols, ethers, esters, and ketones. Water contact angle measurements showed ca. 25% increase in hydrophilicity of the surface with oxidation. Atomic Force Microscopy observed little changes in surface roughness with treatment time. The super water absorbent polymer poly(acrylic acid) was thinly grafted to the modified PS surface.

2710. Li, Y., J. Sun, L. Yao, F. Ji, S. Peng, Z. Gao, and Y. Qiu, “Influence of moisture on effectiveness of plasma treatments of polymer surfaces,” J. Adhesion Science and Technology, 26, 1123-1139, (2012).

In atmospheric pressure plasma treatments water molecules in the substrate material may disrupt the molecular arrangement in the substrate and thus greatly influence the outcome of the plasma treatment. This paper summarizes the results of our recent studies on how moisture influences the etching, surface chemical modification, crystallinity and aging of aramid, ultrahigh molecular weight polyethylene (UHMWPE), polyamide fibers, and poly(vinyl alcohol) (PVA) films. Overall, a higher moisture regain often results in a greatly enhanced etch rate, less surface chemical composition change, increased near-surface crystallinity, which could lead to a higher surface wettability, higher interfacial shear strength between the fibers and resin, decreased water solubility for PVA films, and delayed hydrophobic recovery of plasma treated fibers. Therefore, it is important to control the moisture contained in the substrate in atmospheric pressure plasma treatments.

519. Liao, W.-C., and J.L. Zatz, “Surfactant solutions as test liquids for measurements of critical surface tension,” J. Pharmaceutical Science, 68, 486-488, (1979).

Contact angles of various liquids and surfactant solutions on polytef and paraffin were measured. Critical surface tension values were obtained by extrapolation of plots of cosine of the contact angles versus corresponding surface tension values. Contact angles measured using polyoxyethylene octylphenols produced linear Zisman plots and yielded critical surface tensions that agreed with accepted values. This liquid series provides a reasonable approach to the measurement of critical surface tension for solid drugs that are soluble in organic liquids but relatively insoluble in water.

952. Liebel, G., “Plasma activation: Industrial technology for large-scale treatment of polypropylene, polyethylene and polypropylene/ethylene-propylene terpolymer (EPDM) parts,” Technics Plasma, 0.

765. Liggieri, L., and F. Ravera, “Capillary pressure tensiometry with applications in microgravity,” in Drops and Bubbles in Interfacial Research, Mobius, D., and R. Miller, eds., 239-278, Elsevier, Jun 1998.

The CPT has consequently been employed with several configurations and with different methodologies to measure the interfacial tension of pure liquids and for studying the dynamics of adsorption on different time scales both on earth and in microgravity. Some of these methodologies are described in detail, discussing the critical aspects and the main experimental results. Capillary Pressure (CP) tensiometry is especially helpful for studying liquid/liquid interfaces. Microgravity represents an ideal tool for studying the dynamic aspects of adsorption of soluble surfactants and the CP tensiometry is the most suitable technique for these kind of studies in this environment, both for liquid-liquid and liquid-vapor interfaces. However, provided that the Bond number is sufficiently small, CP tensiometry can also be used in normal laboratory conditions.

2912. Lightfoot, T., “There's more than one way to treat a film,” PFFC, 27, 26-28, (Jul 2022).

2031. Lim, H., Y. Lee, S. Han, and J. Cho, “Surface treatment and characterization of PMMA, PHEMA, and PHPMA,” J. Vacuum Science and Technology A, 19, 1490-1496, (Jul 2001).

Poly(methylmethacrylate) (PMMA), poly(2-hydroxyethyl methacrylate (PHEMA), and poly(2-hydroxypropyl methacrylate) (PHPMA) were modified to improve the wettability by two techniques: plasma and plasma source ion implantation. The modified surfaces were characterized to investigate the dependence of the modification and hydrophobic recovery on the polymer structure. The differences obtained under optimal experiment conditions among the polymers were interpreted in terms of their polymer structures including the glass transition temperature. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. The PSII treatment created more functional groups on the surface and extensively modified the polymer layer than the plasma treatment.

1867. Lin, D.G., “Layer-by-layer modification of thermoplastic coatings to improve adhesion,” J. Adhesion Science and Technology, 11, 1563-1575, (1997).

One of the causes leading to low bond strength between a coating and a substrate (adhesion strength) - if coatings are formed at elevated temperatures in air - is assumed to be a weak boundary layer generated in the region of adhesional contact: the boundary layer consisting mostly of low-molecular-weight products resulting from thermal oxidative degradation of the polymer. It has been verified experimentally that products of oxidation diffuse from the coating surface layer to the contact area. The oxidation process is supposed to be localized within that surface layer. A method has been devised to determine the thickness of the layer, and model experiments have been conducted to show that low-molecular-weight products of oxidation deteriorate the adhesion strength. Ways have been found to increase the adhesion strength of coatings by means of modification of the coating applied in a layer-by-layer manner. The idea is to introduce separately such modifiers as antioxidants, inorganic fillers possessing high adsorption capacities, and crosslinking agents into the coating surface layer. This method of coating modification allows one to eliminate the negative effects of the low-molecular-weight products generated in the surface layers during the formation.

1304. Lin, F.Y.H., D. Li, and A.W. Neumann, “Effect of surface roughness on the dependence of contact angles on drop size,” J. Colloid and Interface Science, 159, 86-95, (1993).

Absence of drop size dependence of contact angles of sessile drop systems is sometimes observed in experiments. The contact angle data sometimes fluctuate periodically about a horizontal line. Moreover, in cases where a drop size dependence of contact angles exists, the contact angle data often scatter significantly. These fluctuations may be caused by surface roughness. In this paper, two idealized rough surface models are developed. The mean contact angle of a sessile drop in each rough solid surface model is calculated. The fluctuations of the drop size dependence of contact angles produced by these models resemble those obtained experimentally and the fluctuations may therefore be a consequence of the roughness on solid surfaces. It is also concluded that the apparent absence of drop size dependence of contact angles does not necessarily imply zero or extremely low line tension.

1033. Lin, G., W. Wenig, and J. Petermann, “Influence of thermal treatment on the adhesion of polypropylene/ethylene-propylene copolymer interfaces,” Angewandte Makromolekulare Chemie, 255, 33-36, (Mar 1998).

The influence of thermal treatment on the adhesion between isotactic poly(propylene) (iPP) and ethylene-propylene copolymer has been studied. The adhesive force between the polymer films was measured by performing peel tests. It was found that an interface layer has been formed. Its structure and thickness are dependent on the thermal history of the sample: the peel strength increases with annealing temperature and time, and the cooling rate, too, influences the peel strength. The method of preparing the iPP films has an effect on the adhesion of the sandwich sample as well.

2793. Lin, K., M. Vuckovac, M. Latikka, T. Huhtamiiki, and R.H.A. Ras, “Improving surface-wetting characterization,” Science, 363, 1147-1148, (Mar 2019).

Highly hydrophobic surfaces have numerous useful properties; for example, they can shed water, be self-cleaning, and prevent fogging (1, 2). Surface hydrophobicity is generally characterized with contact angle (CA) goniometry. With a history of more than 200 years (3), the measurement of CAs was and still is considered the gold standard in wettability characterization, serving to benchmark surfaces across the entire wettability spectrum from superhydrophilic (CA of 0°) to superhydrophobic (CA of 150° to 180°). However, apart from a few reports [e.g., (48)], the inherent measurement inaccuracy of the CA goniometer has been largely overlooked by its users. The development of next-generation liquid-repellent coatings depends on raising awareness of the limitations of CA measurements and adopting more sensitive methods that measure forces.

2521. Lin, T.-K., S.-J. Wu, C.-K. Peng, and C.-H. Yeh, “Surface modification of polytetrafluoroethylene films by plasma pretreatment and graft copolymerization to improve their adhesion to bismaleimide,” Polymer International, 58, 46-53, (Jan 2009).

BACKGROUND: Polytetrafluoroethylene (PTFE) is utilized in many engineering applications, but its poor wettability and adhesion properties with other materials have limited its use. The study reported was aimed at achieving surface modification of PTFE films by radiofrequency NH3 and N2 plasma treatment, followed by graft copolymerization, in order to improve the interfacial adhesion of PTFE and bismaleimide.

RESULTS: X-ray photoelectron spectroscopy results showed that a short-time plasma treatment had a distinct defluorination effect and led to nitrogen functional group formation. The nitrogen chemical bonding form was different for NH3 and N2 plasma treatments. Under the same experimental conditions, the NH3 plasma exhibited a better etching effect than did the N2 plasma. Contact angle measurement showed an improvement in both surface energy and wettabliity by short-time plasma treatment. The concentration of the surface-grafted bismaleimide on PTFE increased after the plasma pretreatment. The lap shear strength between PTFE and bismaleimide increased significantly after surface modification.

CONCLUSION: This study found that plasma treatment caused changes in surface chemistry, thus leading to an increase of the wettability of PTFE surfaces. Hence, the adhesion properties of PTFE with bismaleimide were significantly improved. Copyright © 2008 Society of Chemical Industry

222. Lindholm, G., “Ink transfer in flexo,” Flexo, 23, 40-45, (Feb 1998).

759. Lindland, H.T., “Flame surface treatment,” in Coatings Technology Handbook, Satas, D., ed., 287-294, Marcel Dekker, 1991 (also in Coatings Technology Handbook, 2nd Ed., D. Satas and A.A. Tracton, eds., p. 343-350, Marcel Dekker, Jan 2001, and Coatings Technology: Fundamentals, Testing, and Processing Techniques, A.A. Tracton, ed., p. 39/1-39/7, CRC Press, Oct 2006).

223. Lindland, H.T., and C. Granville, “New developments in flame treating,” in Polymers, Laminations and Coatings Conference Proceedings 1999 (Book 2), TAPPI Press, Aug 1990.

1383. Lindland, T., and A. Peach, “Substrate preparation through direct flame,” in 1985 TAPPI Polymers, Laminations and Coatings Conference Proceedings, TAPPI Press, Aug 1985.

2960. Lindner, M., N. Rodler, M. Jesdinszki, M. Schmid, and S. Sangerlaub, “Surface energy of corona treated PP, PE and PET films, its alteration as function of storage time and the effect of various corona dosages on their bond strength after lamination,” J. Applied Polymer Science, 135, 1-9, (Mar 2018).

The aim of this study was to analyze how corona dosages above recommended levels affect film surface energy and hydrophobic recovery of such treated film surfaces as well as laminate bond strength of laminates made of these films. The adhesive for lamination was a polyurethane-adhesive with a dry film thickness of ∼5 µm. Polar and dispersive parts of the surface energy were measured frequently according to DIN 55660-2 (Owens–Wendt–Rabel-and-Kaelble method) for up to 140 days after corona treatment. The corona dosage had a value of up to 280 W min/m2. Laminate bond strength was measured according to DIN 55543-5. The effect of corona treatment was highest for low-density polyethylene (PE-LD) films, mean for biaxial-oriented polypropylene (PP-BO) films, and lowest for biaxial-oriented poly(ethylene terephthalate) (PET-BO) films. With increasing storage time, surface energy decreased, as expected. The higher the effect of corona treatment, the faster the polar part of surface energy decreased. At PE-LD, laminate bond strength increased with a higher corona dosage from 0.05 to 8.87 mN/15 mm, whereas at PET-BO and PP-BO laminate bond strength was so high that samples teared before delamination during bond strength testing. By our results is shown that corona dosages above recommended levels resulted in higher laminate bond strength. Only at PP-BO a reduction of laminate bond strength due to “overtreatment” was be observed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45842.

224. Lindsay, K.F., “Process surface-treats PP parts in line, opening market opportunities,” Modern Plastics, 69, 47-48, (Apr 1992).

644. Lipatov, Y., and A. Feinerman, “Surface tension and surface free energy of polymers,” Advances in Colloid and Interface Science, 11, 195+, (1979).

The curent state of problems connected with the definition and experimental determination of surface free energy and surface tension of polymers is discussed. An analysis of the application of some equations based on classical and modern thermodynamics of polymer solutions shows that present theories need an essential improvement to fit experimental data. The Zisman concept of critical surface tension and Fowkers' hypothesis of additivity in the contribution of polar and dispersion forces to surface tension are criticized and a new approach to the problem is proposed.

645. Liston, E.M., “Plasma modification of polymer surfaces,” in Polymer - Solid Interfaces, Pireaux, J.J., P. Bertrand, and J.L. Bredas, eds., 429-454, Institute of Physics Publishing, 1991.

1350. Liston, E.M., “Plasma treatment for improved bonding: a review,” J. Adhesion, 30, 199-218, (1989).

The nature of low-pressure glow-discharge plasma, plasma equipment, and the effect of plasma on materials is reviewed. Examples are given of the improved adhesive bonding of polymers after plasma treatment (2–10 times improvement in lap-shear) and of the surface cleaning and chemical modification that occurs during plasma treatment.

825. Liston, E.M., L. Martinu, and M.R. Wertheimer, “Plasma surface modification of polymers for improved adhesion: a critical review,” J. Adhesion Science and Technology, 7, 1091-1127, (1993) (also in Plasma Surface Modification of Polymers: Relevance to Adhesion. M. Strobel, C.S. Lyons, and K.L. Mittal, eds., p. 3-42, VSP, Oct 1994).

1589. Liston, E.M., and M.R. Wertheimer, “Plasma surface modification of polymers for improved adhesion: a critical review,” J. Adhesion Science and Technology, 7, 1091-1127, (1993).

Since the earliest systematic research during the 1960s, the field of materials surface modification by 'cold', low-pressure plasma treatment has undergone an enormous expansion. Much of this expansion has taken place in recent years, particularly in the surface modification of polymeric materials, for which there now exist numerous industrial applications (enhancement of paint adhesion, improved bonding in polymer matrix composites, etc.). In this paper, we provide a critical review of the development and trends in this field; reference is also made to other surface modification techniques, particularly to corona treatment, and comparisons are made wherever appropriate. We begin with a brief overview of adhesion theory, and of the physics and chemistry of 'cold' plasmas. Next, interaction mechanisms between a plasma and a polymer surface are examined; these include physical bombardment by energetic particles and by ultraviolet photons, and chemical reactions at or near the surface. The resulting four main effects, namely cleaning, ablation, crosslinking, and surface chemical modification, occur together in a complex synergy, which depends on many parameters controlled by the operator. In spite of this complexity, for there are still many unanswered questions, it is nevertheless possible to optimize the main set of parameters governing a given process, and then to reliably reproduce the process outcome. Three industrially important systems, for which many research results exist, are then separately examined, namely: (i) polymer-polymer bonding, (ii) polymer-matrix composites, and (iii) metal-polymer bonding. Finally, we present a brief overview of commercial plasma reactors for industrial (non-semiconductor) purposes, and of process considerations for efficient use of such equipment. We foresee that the use of plasma processes will continue to expand, because they have unique capabilities, are economically attractive, and are 'friendly' towards the environment.

2548. Little, U., F. Buchanon, E. Harkin-Jones, B. Graham, B. Fox, et al, “Surface modification of poly(epsilon-capralactone) using a dielectric barrier discharge in atmospheric pressure glow discharge mode,” Acto Biomaterialia, 5, 2025-2032, (Jul 2009).

The role of roughening and functionalization processes involved in modifying the wettability of poly(ε-caprolactone) (PCL) after treatment by an atmospheric pressure glow discharge plasma is discussed. The change in the ratio of CDouble BondO/C–O bonds is a significant factor influencing the wettability of PCL. As the contact angle decreases, the level of CDouble BondO bonds tends to rise. Surface roughness alterations are the driving force for lasting increases in wettability, while the surface functional species are shorter lived. We can approximate from ageing that the increase in wettability for PCL after plasma treatment is 55–60% due to roughening and 40–45% due to surface functionalization for the plasma device investigated.

520. Liu, D., “Surface modification of polystyrene by plasma treatment (MS thesis),” Univ. of Massachusetts, 1991.

1756. Liu, Y., H. Xu, L. Ge, C. Wang, L. Han, H. Yu, and Y. Qiu, “Influence of environmental moisture on atmospheric pressure plasma jet treatment of ultrahigh-modulus polyethylene fibers,” J. Adhesion Science and Technology, 21, 663-676, (2007).

One of the main differences between low-pressure and atmospheric-pressure plasma treatments is that there is little moisture involved in the low-pressure plasma treatment, although moisture could exist at the wall of the vacuum chamber or react with the substrate after plasma treatment, while in the atmospheric-pressure plasma treatment moisture exists not only in the environment but also in any hygroscopic substrate. In order to investigate the influence of environmental moisture on the effect of atmospheric pressure plasma treatment, ultra-high-modulus polyethylene (UHMPE) fibers were treated using an atmospheric-pressure plasma jet (APPJ) with 10 l/min helium gas-flow rate, treatment nozzle temperature of 100°C and 5 W output power. The plasma treatments were carried out at three different relative humidity levels, namely 5, 59 and 100%. After the plasma treatments, the surface roughness increased while the water-contact angle decreased with increasing relative humidity. The number of oxygen containing groups increased as the environmental moisture content increased. The interfacial shear strength of the UHMPE fiber/epoxy system was significantly increased after the plasma treatments, but the moisture level in the APPJ environment did not have a significant influence on the adhesion properties. In addition, no significant difference in single fiber tensile strength was observed after the plasma treatments at all moisture levels. Therefore, it was concluded that the environmental moisture did not significantly influence the effect of atmospheric-pressure plasma treatment in improving interfacial bonding between the fiber and epoxy. The improvement of the interfacial shear strength for the plasma-treated samples at all moisture levels was mainly due to the increased surface roughness and increased surface oxygen and nitrogen contents due to the plasma etching and surface modification effect.

1169. Liu, Y., and D. Lu, “Surfcae energy and wettability of plasma-treated polyacrylonitrile fibers,” Plasma Chemistry and Plasma Processing, 26, 119-126, (Apr 2006).

Polyacrylonitrile fibers were treated with a nitrogen glow-discharge plasma. The surfaces of untreated and treated fibers were examined with contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Surface energy calculations of the fibers were carried out from contact angle measurements using the relationships developed by Fowkes. It is found that plasma treatment causes a reduction in water contact angle on the fiber surfaces. The dispersion component of surface energy changes slightly, while the polar component is increased significantly from 14.6 mN/m to 58.7 mN/m and the total surface energy increase is 139%. The increase of surface energy is mainly caused by the introduction of hydrophilic groups on the fiber surfaces after plasma treatment.

2085. Lommatzsch, U., D. Pasedag, A. Baalmann, G. Ellinghorst, and H.-E. Wagner, “Atmospheric pressure plasma jet treatment of polyethylene surfaces for adhesion improvement,” Plasma Processes and Polymers, 4, S1041-S1045, (2007).

Polyethylene (PE) samples were activated by an atmospheric pressure plasma jet. The improvement in adhesive bond strength is attributed to the incorporation of oxygen-containing functional groups into the PE surface. Optical emission spectroscopy in combination with XPS analysis shows differences in the surface reactions for a plasma jet operated with air or pure nitrogen. The results indicate that the surface modifications take place in two different environments with respect to location and time: (a) reactions while the substrate is hit by the plasma jet, and (b) reactions outside the plasma jet after the treatment.

1560. Lommatzsch, U., M. Noeske, J. Degenhart, T. Wubben, S. Strudthoff, et al, “Pretreatment and surface modification of polymers via atmospheric-pressure plasma jet treatment,” in Polymer Surface Modification: Relevance to Adhesion, Vol. 4, K.L. Mittal, ed., 25-32, VSP, May 2007.

A novel atmospheric pressure plasma jet, that is operated with air, is used for the pretreatmet of different polymers. The resulting adhesive bond strengths and the corresponding changes of the polymer substrate surface are studied. The plasma treatment induces chemical and topographical changes on the polymer surface. It is likely that both types of surface modification contribute to the adhesion improvement. Results for poly (ethylene terephthalate) indicate that surface chemical composition is more influential in adhesion enhancement than surface roughness.

1119. Long, J., and P. Chen, “Thermodynamics of contact angles on rough, heterogeneous surfaces,” in Molecular Interfacial Phenomena of Polymers and Biopolymers, Chen, P., ed., 119-158, Woodhead Publishing, Sep 2005.

This chapter presents a comprehensive study on the thermodynamics of contact angles on general rough, heterogeneous surfaces. Conventionally, contact is defined as the angle formed between a liquid-vapor interface and a liquid-solid interface at the solid-liquid-vapor three-phase contact line. On an ideal solid surface, which is smooth, homogeneous, isotropic, and non-deformable, the contact angle is expressed by the Young equation. The concept of liquid front simplified the thermodynamic treatments of contact angles on rough, heterogeneous surfaces and thus made it possible to model real surfaces. Receding contact angles are poorly reproducible for hydrophilic surfaces but for extremely hydrophobic surfaces, advancing contact angles might have a poor reproducibility. An impurity might cause poor reproducibility for receding contact angles if it is the component with the smallest intrinsic contact angle, but it can make the advancing contact angle. An impurity might not affect contact angle hysteresis if it is the component with an intermediate intrinsic contact angle.

2549. Lopez-Santos, C., F. Yubero, J. Cotrino, and A.R. Gonzalez-Elipe, “Surface functionalization, oxygen depth profiles, and wetting behavior of PET treated with different nitrogen plasmas,” Applied Material Interfaces, 2, 980-990, (2010).

Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N2 and mixtures Ar + NH3 as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard’s method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH3 is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization by reaction with chlorobenzaldehyde. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated PET.

2378. Lori, G., “Method of flame activation of substrates,” U.S. Patent 4622237, Nov 1986.

2360. Lough, J.C., “Reducing flame treatment of polyethylene terephthalate film prior to metalization,” U.S. Patent 3431135, Mar 1969.

225. Lub, J., F.C.B.M. van Vroohoven, E. Brunnix, and A. Benninghoven, “Interaction of nitrogen and ammonia plasmas with polystyrene and polycarbonate studied by X-ray photoelectron spectroscopy, neutron activation analysis and static secondary ion mass spectrometry,” Polymer, 30, 40-44, (1989).

The interactions of NH3 and N2 plasmas with the surfaces of polystyrene (PS) and bisphenol-A polycarbonate (PC) have been studied with X.p.s. and SSIMS. Primary amino groups could be detected at the surfaces of both polymers after treatment with the NH3 plasma but not with the N2 plasma, with the aid of derivatization reactions with salicylaldehyde and 5-bromosalicylaldehyde. PC differs in its reactivity from PS with respect to its ease of undergoing chain scission during the plasma treatments, which results in modified structures of low molecular weight at the surface. The surface coverage of primary amino groups on PS after treatment with the NH3 plasma was determined by means of neutron activation analysis after derivatization of these groups with 5-bromosalicylaldehyde and estimated to be approximately 0.5 amino groups per nm2.


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